Optical correction systems and methods for correcting non-uniformity of emissive display devices

ABSTRACT

What is disclosed are systems and methods of optical correction for pixel evaluation and correction for active matrix light emitting diode device (AMOLED) and other emissive displays. Optical correction for correcting for non-homogeneity of a display panel uses sparse display test patterns in conjunction with a defocused camera as the measurement device to avoid aliasing (moire) of the pixels of the display in the captured images.

FIELD OF THE INVENTION

The present disclosure relates to optically measuring and calibratinglight emissive visual display technology, and particularly to opticalcorrection systems and methods for individual pixel luminance evaluationand correction for active matrix organic light emitting diode device(AMOLED) and other emissive displays.

BRIEF SUMMARY

According to a first aspect there is provided an optical correctionmethod for correcting for non-uniformity of an emissive display panelhaving pixels, each pixel having a light-emitting device, the methodcomprising: arranging a camera in front of the display panel; defocusingthe camera such that the focal point of the camera lies outside of aplane passing through the light-emitting devices of the display panel,the defocusing such that individual pixels of the display panel areblurred in images of the display panel captured by the camera;displaying a plurality of test patterns while capturing respectiveimages of said test patterns displayed, said captured images for use asluminance measurement data for pixels of the display panel, each of saiddisplayed test patterns comprising a set of activated pixels spacedapart such that in each captured image, at least one portion of eachblurred image of each activated pixel does not overlap with a blurredimage of another activated pixel; and determining from said luminancemeasurement data, correction data for correcting non-uniformity ofimages displayed in the display panel.

In some embodiments, the amount of blurring in images of the displaypanel captured by the camera is sufficient to avoid aliasing in thecaptured images of the display panel.

In some embodiments, a resolution of the camera is less than twice aresolution of the display panel. In some embodiments, said activatedpixels of each displayed test pattern are arranged in a diamond orrectangular lattice.

In some embodiments, said activated pixels of the plurality of displayedtest patterns comprise regular test pixels, each of said regular testpixels of said plurality of displayed test patterns having a greyscaleluminance value selected from a set of at least two predeterminedgreyscale luminance values. In some embodiments, the set of at least twopredetermined greyscale luminance values includes a relatively lowgreyscale luminance value and a relatively high greyscale luminancevalue.

In some embodiments, said activated pixels of the plurality of thedisplayed test patterns comprise multilevel pixels, each of saidmultilevel pixels of said plurality of displayed test patterns having agreyscale luminance value greater or less than one of the greyscaleluminance values of the set of at least two predetermined greyscaleluminance values by a relatively small greyscale luminance value.

Some embodiments further provide for determining correction data foreach pixel of the display panel with use of a first luminancemeasurement of that pixel when displaying a first greyscale luminancevalue of the set of at least two predetermined greyscale luminancevalues and a second luminance measurement of that pixel when displayinga second greyscale luminance value of the set of at least twopredetermined greyscale luminance values, and with use of a scale factorfor that pixel determined with use of luminance measurements of pixelsthroughout the display panel when displaying the multilevel pixels ofthe displayed test patterns.

In some embodiments, said activated pixels of the plurality of thedisplayed test patterns comprise calibration pixels, the embodimentfurther providing for determining locations of the activated pixels ofthe displayed test patterns as they appear in the captured images of thedisplayed test patterns; and determining at least one point spreadfunction exhibited by blurred images of activated pixels of thedisplayed test pattern in the captured images, in which the activatedpixels of the plurality of displayed test patterns are spaced apart suchthat in the captured images, blurred images of each calibration pixeldoes not overlap with blurred images of any other activated pixel.

In some embodiments, each of the luminance measurements of each of theregular test pixels and each of the multilevel pixels is performed withuse of an acquisition kernel determined from at least one of a spacingof the activated pixels of the displayed test patterns and the at leastone point spread function.

In some embodiments, the relatively low greyscale luminance value issubstantially 10 percent of the maximum possible greyscale luminancevalue, and the relatively high greyscale luminance value issubstantially 80 percent of the maximum greyscale luminance value. Insome embodiments, the relatively small greyscale luminance value is oneof substantially 1 percent of the maximum possible greyscale luminancevalue and the smallest incremental digital value of possible greyscaleluminance values.

In some embodiments, all of said regular test pixels of the relativelylow greyscale luminance value are displayed in a first set of sparseflat test patterns, wherein all of said regular test pixels of therelatively high greyscale luminance value are displayed in a second setof sparse flat test patterns, wherein all of said multilevel pixelshaving a greyscale luminance value greater or less than the relativelylow greyscale luminance value are displayed in a first set of multilevelpatterns, and wherein all of said multilevel pixels having a greyscaleluminance value greater or less than the relatively high greyscaleluminance value are displayed in a second set of multilevel patterns.

Some embodiments further provide for correcting image data with use ofthe correction data prior to driving the pixels to display an imagecorresponding to the image data.

According to a second aspect there is provided an optical correctionsystem for correcting non-uniformity of an emissive display havingpixels, each pixel having a light-emitting device, the systemcomprising: a camera arranged in front of the display for capturingimages of a plurality of test patterns displayed on the display, thecamera defocused such that the focal point of the camera lies outside ofa plane passing through the light-emitting devices of the display andsuch that individual pixels of the display are blurred in images of thedisplay captured by the camera, each of said displayed test patternscomprising a set of activated pixels spaced apart such that in eachcaptured image, at least one portion of each blurred image of eachactivated pixel does not overlap with a blurred image of anotheractivated pixel; optical correction processing coupled to the camera andfor receiving from the camera captured images of said test patternsdisplayed on the display, said captured images for use as luminancemeasurement data for pixels of the display; determining from saidluminance measurement data, correction data for correctingnon-uniformity of images displayed in the display; and transmitting thecorrection data to the display for storage in a memory of the display.

In some embodiments, the optical correction processing is further fordetermining correction data for each pixel of the display with use of afirst luminance measurement of that pixel when displaying a firstgreyscale luminance value of the set of at least two predeterminedgreyscale luminance values and a second luminance measurement of thatpixel when displaying a second greyscale luminance value of the set ofat least two predetermined greyscale luminance values, and with use of ascale factor for that pixel determined with use of luminancemeasurements of pixels throughout the display when displaying themultilevel pixels of the displayed test patterns.

In some embodiments, said activated pixels of the plurality of thedisplayed test patterns comprise calibration pixels, and wherein theoptical correction processing is further for determining locations ofthe activated pixels of the displayed test patterns as they appear inthe captured images of the displayed test patterns; and determining atleast one point spread function exhibited by blurred images of activatedpixels of the displayed test pattern in the captured images, wherein theactivated pixels of the plurality of displayed test patterns are spacedapart such that in the captured images, blurred images of eachcalibration pixel does not overlap with blurred images of any otheractivated pixel.

In some embodiments, each of the luminance measurements of each of theregular test pixels and each of the multilevel pixels is performed bythe optical correction processing with use of an acquisition kerneldetermined from at least one of a spacing of the activated pixels of thedisplayed test patterns and the at least one point spread function.

Some embodiments, further provide for a controller of the emissivedisplay system coupled to said optical correction processing, saidcontroller for receiving image data for display by the display;receiving from the optical correction processing the correction data;and correcting the image data with use of the correction data prior todriving the pixels to display an image corresponding to the image data.

The foregoing and additional aspects and embodiments of the presentdisclosure will be apparent to those of ordinary skill in the art inview of the detailed description of various embodiments and/or aspects,which is made with reference to the drawings, a brief description ofwhich is provided next.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the disclosure will becomeapparent upon reading the following detailed description and uponreference to the drawings.

FIG. 1 illustrates an example display system which participates in andwhose pixels are to be measured and corrected by the optical correctionsystems and methods disclosed;

FIG. 2 is a system block diagram of an optical correction system;

FIG. 3 is a high level functional block diagram of an optical correctionmethod; and

FIG. 4 illustrates an example method of displaying and capturing displaytest patterns of the method illustrated in FIG. 3.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments or implementations have beenshown by way of example in the drawings and will be described in detailherein. It should be understood, however, that the disclosure is notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of an invention as defined by theappended claims.

DETAILED DESCRIPTION

Many modern display technologies suffer from defects, variations, andnon-uniformities, from the moment of fabrication, and can suffer furtherfrom aging and deterioration over the operational lifetime of thedisplay, which result in the production of images which deviate fromthose which are intended. Optical correction systems and methods can beused, either during fabrication or after a display has been put intouse, to measure and correct pixels (and sub-pixels) whose outputluminance varies from the expected luminance. AMOLED panels inparticular are characterized by luminance non-uniformity.

To correct for this intrinsic non-uniformity of the display, theincoming video signal is deliberately modified with compensation data orcorrection data such that it compensates for the non-uniformity. In someapproaches, to obtain the correction data the luminance of eachindividual panel pixel is measured for a range of greyscale luminancevalues, and correction values for each pixel are determined. A typicalsetup utilizes a monochrome or conventional RGB still picture camera asthe measurement device. At least one calibration pattern is displayed onthe display and captured with the camera. Measurements in the form ofcaptured images are then processed to extract the actual luminance ofeach individual pixel of the display. Taking into account the greyscaleluminance value of the pixel of the calibration pattern which was usedto drive the pixel of the display, a correction signal for that pixel ofthe display driven at that greyscale luminance value is generated.Limitations with this technique arise when the spatial sampling rate ofthe camera falls below two times the spatial frequency of the pixelimage of the display. According to well-known sampling principles, thecamera should operate at or above the Nyquist rate, i.e. at or abovetwice the frequency of the pixel image of the display, in order toreconstruct the displayed image accurately from a single captured imagetaken by the camera. When the sampling rate of the camera falls belowtwice the image pixel rate of the display, the reconstructed image willsuffer from aliasing (moire) and pixel overlap, i.e. images of differentpixels of the display will overlap in images taken by the camera. Asdisplays are produced with increasingly higher and higher resolutionsthis poses a problem for obtaining correction data with existingstandard resolution cameras which do not have resolutions as high astwice as that of the display, and alternatively increases costs bynecessitating deployment of optical correction systems which includemuch higher resolution cameras.

While the embodiments described herein will be in the context of AMOLEDdisplays it should be understood that the optical correction systems andmethods described herein are applicable to any other display comprisingpixels, including but not limited to light emitting diode displays(LED), electroluminescent displays (ELD), organic light emitting diodedisplays (OLED), plasma display panels (PSP), microLED or quantum dotdisplays, among other displays.

It should be understood that the embodiments described herein pertain tosystems and methods of optical correction and compensation and do notlimit the display technology underlying their operation and theoperation of the displays in which they are implemented. The systems andmethods described herein are applicable to any number of various typesand implementations of various visual display technologies.

FIG. 1 is a diagram of an example display system 150 implementing themethods described further below in conjunction with an arrangement witha camera and optical correction processing. The display system 150includes a display panel 120, an address driver 108, a data driver 104,a controller 102, and a memory storage 106.

The display panel 120 includes an array of pixels 110 (only oneexplicitly shown) arranged in rows and columns. Each of the pixels 110is individually programmable to emit light with individuallyprogrammable luminance values. The controller 102 receives digital dataindicative of information to be displayed on the display panel 120. Thecontroller 102 sends signals 132 to the data driver 104 and schedulingsignals 134 to the address driver 108 to drive the pixels 110 in thedisplay panel 120 to display the information indicated. The plurality ofpixels 110 of the display panel 120 thus comprise a display array ordisplay screen adapted to dynamically display information according tothe input digital data received by the controller 102. The displayscreen and various subsets of its pixels define “display areas” whichmay be used for monitoring and managing display brightness. The displayscreen can display images and streams of video information from datareceived by the controller 102. The supply voltage 114 provides aconstant power voltage or can serve as an adjustable voltage supply thatis controlled by signals from the controller 102. The display system 150can also incorporate features from a current source or sink (not shown)to provide biasing currents to the pixels 110 in the display panel 120to thereby decrease programming time for the pixels 110.

For illustrative purposes, only one pixel 110 is explicitly shown in thedisplay system 150 in FIG. 1. It is understood that the display system150 is implemented with a display screen that includes an array of aplurality of pixels, such as the pixel 110, and that the display screenis not limited to a particular number of rows and columns of pixels. Forexample, the display system 150 can be implemented with a display screenwith a number of rows and columns of pixels commonly available indisplays for mobile devices, monitor-based devices, and/orprojection-devices. In a multichannel or color display, a number ofdifferent types of pixels, each responsible for reproducing color of aparticular channel or color such as red, green, or blue, will be presentin the display. Pixels of this kind may also be referred to as“subpixels” as a group of them collectively provide a desired color at aparticular row and column of the display, which group of subpixels maycollectively also be referred to as a “pixel”.

The pixel 110 is operated by a driving circuit or pixel circuit thatgenerally includes a driving transistor and a light emitting device.Hereinafter the pixel 110 may refer to the pixel circuit. The lightemitting device can optionally be an organic light emitting diode, butimplementations of the present disclosure apply to pixel circuits havingother electroluminescence devices, including current-driven lightemitting devices and those listed above. The driving transistor in thepixel 110 can optionally be an n-type or p-type amorphous siliconthin-film transistor, but implementations of the present disclosure arenot limited to pixel circuits having a particular polarity of transistoror only to pixel circuits having thin-film transistors. The pixelcircuit 110 can also include a storage capacitor for storing programminginformation and allowing the pixel circuit 110 to drive the lightemitting device after being addressed. Thus, the display panel 120 canbe an active matrix display array.

As illustrated in FIG. 1, the pixel 110 illustrated as the top-leftpixel in the display panel 120 is coupled to a select line 124, a supplyline 126, a data line 122, and a monitor line 128. A read line may alsobe included for controlling connections to the monitor line. In oneimplementation, the supply voltage 114 can also provide a second supplyline to the pixel 110. For example, each pixel can be coupled to a firstsupply line 126 charged with Vdd and a second supply line 127 coupledwith Vss, and the pixel circuits 110 can be situated between the firstand second supply lines to facilitate driving current between the twosupply lines during an emission phase of the pixel circuit. It is to beunderstood that each of the pixels 110 in the pixel array of the display120 is coupled to appropriate select lines, supply lines, data lines,and monitor lines. It is noted that aspects of the present disclosureapply to pixels having additional connections, such as connections toadditional select lines, and to pixels having fewer connections.

With reference to the pixel 110 of the display panel 120, the selectline 124 is provided by the address driver 108, and can be utilized toenable, for example, a programming operation of the pixel 110 byactivating a switch or transistor to allow the data line 122 to programthe pixel 110. The data line 122 conveys programming information fromthe data driver 104 to the pixel 110. For example, the data line 122 canbe utilized to apply a programming voltage or a programming current tothe pixel 110 in order to program the pixel 110 to emit a desired amountof luminance. The programming voltage (or programming current) suppliedby the data driver 104 via the data line 122 is a voltage (or current)appropriate to cause the pixel 110 to emit light with a desired amountof luminance according to the digital data received by the controller102. The programming voltage (or programming current) can be applied tothe pixel 110 during a programming operation of the pixel 110 so as tocharge a storage device within the pixel 110, such as a storagecapacitor, thereby enabling the pixel 110 to emit light with the desiredamount of luminance during an emission operation following theprogramming operation. For example, the storage device in the pixel 110can be charged during a programming operation to apply a voltage to oneor more of a gate or a source terminal of the driving transistor duringthe emission operation, thereby causing the driving transistor to conveythe driving current through the light emitting device according to thevoltage stored on the storage device.

Generally, in the pixel 110, the driving current that is conveyedthrough the light emitting device by the driving transistor during theemission operation of the pixel 110 is a current that is supplied by thefirst supply line 126 and is drained to a second supply line 127. Thefirst supply line 126 and the second supply line 127 are coupled to thevoltage supply 114. The first supply line 126 can provide a positivesupply voltage (e.g., the voltage commonly referred to in circuit designas “Vdd”) and the second supply line 127 can provide a negative supplyvoltage (e.g., the voltage commonly referred to in circuit design as“Vss”). Implementations of the present disclosure can be realized whereone or the other of the supply lines (e.g., the supply line 127) isfixed at a ground voltage or at another reference voltage.

The display system 150 also includes a monitoring system 112. Withreference again to the pixel 110 of the display panel 120, the monitorline 128 connects the pixel 110 to the monitoring system 112. Themonitoring system 12 can be integrated with the data driver 104, or canbe a separate stand-alone system. In particular, the monitoring system112 can optionally be implemented by monitoring the current and/orvoltage of the data line 122 during a monitoring operation of the pixel110, and the monitor line 128 can be entirely omitted. The monitor line128 allows the monitoring system 112 to measure a current or voltageassociated with the pixel 110 and thereby extract information indicativeof a degradation or aging of the pixel 110 or indicative of atemperature of the pixel 110. In some embodiments, display panel 120includes temperature sensing circuitry devoted to sensing temperatureimplemented in the pixels 110, while in other embodiments, the pixels110 comprise circuitry which participates in both sensing temperatureand driving the pixels. For example, the monitoring system 112 canextract, via the monitor line 128, a current flowing through the drivingtransistor within the pixel 110 and thereby determine, based on themeasured current and based on the voltages applied to the drivingtransistor during the measurement, a threshold voltage of the drivingtransistor or a shift thereof.

The controller and 102 and memory store 106 together or in combinationwith a compensation block (not shown) use compensation data orcorrection data, in order to address and correct for the variousdefects, variations, and non-uniformities, existing at the time offabrication, and optionally, defects suffered further from aging anddeterioration after usage. In some embodiments, the correction dataincludes data for correcting the luminance of the pixels obtainedthrough measurement and processing using an external optical feedbacksystem such as that described below. Some embodiments employ themonitoring system 112 to characterize the behavior of the pixels and tocontinue to monitor aging and deterioration as the display ages and toupdate the correction data to compensate for said aging anddeterioration over time.

For the embodiments disclosed herein, correction data is directlydetermined during an optical correction operation either during orsubsequent to fabrication or after the display has been in operation forsome time, from observing the luminance of each pixel and determiningthe correction data to produce luminance of an acceptable level.

Referring to FIG. 2, an optical correction system 200 according to anembodiment will now be described.

The optical correction system 200 includes display system 250 which isto be corrected, a camera 230, a controller 202 for overall control theprocess, which in the embodiment of FIG. 2 is shown as part of thedisplay system 250, and an optical correction processing module 240 forcontrolling specific processes of the optical correction methods. Theoptical correction processing 240 can be part of an external tool thatis used for example in a production factory for correction of thedisplays. In another case, optical correction processing 240 can be partof the display system and/or the controller, for example, integrated ina timing controller TCON. The display system 250 of FIG. 2 maycorrespond more or less to the display system 150 of FIG. 1 and includessimilar components thereof, of which specifically, drivers 207, thedisplay panel 220, and the controller 202 are shown explicitly forconvenience. The controller 202 may correspond to controller 102 orcontroller 102 and memory 106 of FIG. 1.

The camera 230 is arranged to measure the luminance of all of the pixels110 of the display panel 220. The camera 230 may be based on a digitalphotography system with lenses, and may be a monochromatic digitalcamera or a standard digital camera, such as a monochromatic or RGB, CCDCMOS or other sensor array based camera, or any other suitable opticalmeasurement technology capable of taking optical images through a lensand generating a luminance measurement image representative of theoptical output of the display panel 220. Optical correction processing240 receives the luminance measurement image data from the camera 230.Luminance measurement image data refers to any matrix containing opticalluminance data corresponding to the output of the display panel 220, andmay comprise multiple channels such as red (R), green (G), blue (B) etc.and in some cases may be monochromatic as in the case where the camera230 is monochromatic. Hereinafter, luminance measurement image data willbe referred to simply as a “captured image” and if monochromatic, willbe assumed to include one luminance value for every pixel of thecaptured image. It should be understood that any reference made to“greyscale luminance value” is a reference to the DAC (Digital toAnalogue Converter) signal data value used to drive a pixel and whichresults in a pixel producing an actual luminance. For simplicity, thepreset luminance values associated with the various pixel patternsdescribed below are characterized in terms of the corresponding DACsignal i.e. greyscale luminance value which is used to drive the pixels.Advantages of using a monochromatic camera versus an RGB camera includefaster exposure times, avoidance of display and sensor R,G,B frequencymismatch and/or crosstalk, avoidance of mismatching numbers orarrangements of the R,G,B sub-pixels of the display and the R,G,Belements of the sensor array, and ease of handing yellow or whitesubpixels of display panel 220. In some embodiments utilizing either amonochromatic or an RGB camera, measurements of each pixel of thedisplay occurs only for a single channel or subpixel color (R, G, B, Y,or W etc.) at any one time.

For the embodiments herein described, the resolution of the camera 230and equally a ratio of the resolution of the camera 230 to theresolution of the display panel 220, are not required to exceed thethresholds otherwise required according to the Nyquist rate. This isbecause the camera is intentionally defocused and test patternsincorporate activated pixels whose blurred images have portions which donot overlap with one another, as described below. In particular, theresolution of the camera 230 need not be greater than twice theresolution of the display panel 220. The camera 230 may be operatedmanually or automatically controlled by one or both of the controller202 and optical correction processing 240.

With reference also to the optical correction method 300 of FIG. 3,camera 230 and the display panel 220 are arranged 302 such that theentirety of the viewable area of the display panel 220 appears withinthe field of view of the camera 230. In some embodiments, the camera 230is positioned in front of display panel 220, aimed at the center of theviewable area of the display panel 220 and with the viewable area of thedisplay panel 220 maximized to occupy as much of the field of view ofthe camera 230 as possible. The line of sight of the camera 230(controlled by camera pan, tilt, and positioning) may be such that it isparallel and coincident with a normal to the plane of the front surfaceof the display panel 220 emerging at the center of the display panel 220to reduce distortions and to ensure any remaining distortions are assymmetrical as possible in the resulting images of the display panel220. Calibration pattern processing discussed below, however, cancompensate for deviations in the relative placement and alignment of thecamera 230 and the display panel 220.

Once the camera 230 and the display panel 220 have been arranged 302relative to each other, the camera 230 is intentionally defocused 304.The defocusing of the camera 230 results in the focal point of thecamera being positioned either in front of or behind a plane passingthrough the light emitting elements of the pixels 110 of the displaypanel 220. The amount of defocusing is set such that it is sufficient,in the context of the particular display panel 220 and camera 230, toavoid aliasing (moire). This amount of defocusing generally depends upona number of factors, primarily upon the ratio of the resolution of thecamera 230 to the resolution of the display panel 220, but also upon thenumber and arrangement of subpixels per pixel 110 in the display panel220, the number and arrangement of optical sensors (CCD, CMOS, etc.),the presence of color/bayer and/or antialiasing filters in the camera230, and any effects caused by the optics of the front surface layers ofthe display panel 220, etc. The level of defocusing will vary from caseto case, but generally the amount of defocusing which is sufficient toavoid aliasing (moire) is directly determined through empirical testing.In some embodiments the minimum amount of defocusing to completelyremove aliasing is chosen.

Instead of displaying all pixels of the display panel 220 simultaneouslyaccording to known techniques, in combination with intentionaldefocusing, the present embodiments display a number of display testpatterns, each of which includes a sparse set of activated pixels whichare spaced apart far enough so that at least some portion of the blurredimages of each of the activated pixels in the captured images do notoverlap or interfere with each other. Typically this portion wouldinclude (but is not limited to) the center of each blurred image of theactivated pixels, and in some cases this non-overlapping portion wouldconstitute a majority of each blurred image of an activated pixel, inwhich case, only the outer portions or edges of the blurred images ofthe pixels would overlap. In some embodiments, and for some testpatterns, the blurred images of the activated pixels in the capturedimages do not have any overlap with each other. Combining the defocusingwith appropriately spaced apart activated pixels simultaneously avoidsaliasing (moire) while accommodating use of a camera 220 with aresolution well below the Nyquist limit to measure individual pixelluminances. Moreover, by avoiding overlap for at least some portion ofeach image of each pixel, the highest frequency mura may becharacterized i.e. accurate measurements of the luminance on anindividual pixel basis is possible. As described below, even inembodiments with some overlap of the blurred images of the individualpixels, as long as the overlap is controlled, accurate measurements ofthe luminance of each individual pixel may be made with appropriatelychosen acquisition kernals which avoid or processes areas of overlapwith appropriate weights.

In embodiments where the amount of defocusing is chosen to be as smallas possible while still avoiding aliasing (moire), smaller point spreadimages of the activated pixels are created, allowing for a morestreamlined process by involving fewer test patterns each of whichrequires smaller spaces between activated pixels to avoid overlap. Insome embodiments, only individual channels (R, G, B, Y, W etc) of eachactivated pixel are activated at any one time.

Once the camera has been defocused 304 a calibration pattern isdisplayed on the display panel 230 and an image is captured 306 by thecamera 220. In some embodiments, the calibration pattern includes asparse set of single pixels activated differently from a flatbackground. Preferably, in some embodiments, the spacing of the sparseset of single activated pixels of the calibration pattern is such thatthe images of those pixels in images taken by the camera 230 do not haveany overlap. In some embodiments the activated pixels are set at adiscernably bright greyscale and the flat background is black. In someembodiments, only individual channels (e.g. R, G, or B) of any activatedpixel are activated at any one time. In some embodiments, the activatedpixels are arranged in a spaced rectilinear array or a rectangularlattice. In such embodiments the activated pixels are located at cornersof an imaginary grid which would result from imaginary lines drawnthrough the rows and columns of activated pixels and is also known as adot grid. Other regular lattices include triangular, and diamond patternlattices. Any sparse set of activated pixels of sufficient spacing maybe used whether arranged in a regular or irregular lattice. Thecalibration pattern is utilized to establish the location of theindividual pixels on the display panel 220 in the captured images whichare captured by the camera 230. The activated pixels in the calibrationpattern are chosen such that the subpixel layout of the panel issufficiently captured. The center of the activated pixels are thenlocated within the captured image and an nth polynomial approximation isthen performed, to calculate the location of every subpixel on the panelin the image. The distribution and pattern of the locations of thepixels of the calibration pattern as they appear in the captured imagewhich is captured by the camera 230 (hereinafter the “calibrationimage”) allows correction of any geometrical distortion, such asrotation, tilt and skew, in subsequent images of the display panel 220taken by the camera 230. The calibration image also samples the pointspread function (PSF) caused by the defocusing and corresponding to theblurring of pixels located in each area of the image of the displaypanel 220. Although the PSF may be substantially homogeneous across thecaptured images taken of the display panel 220, often due to manyfactors, including the structure of the lens system of the camera 230,the PSF may be non-uniform throughout various areas of the capturedimages of the display panel 220. In the case of a calibration pattern ofsparse individual pixels, the point spread function is substantiallydirectly observable in the image captured by the camera 230. In someembodiments more than one calibration pattern is utilized. In someembodiments, no separate calibration pattern is used, and instead, oneor more of the test patterns discussed below serve the same functions asthe calibration pattern and in other embodiments “calibration pixels”are included within the series of display test patterns and serve thesame function as the calibration pattern. The point spread function maybe utilized in display panel 220 pixel luminance determination asdiscussed below.

In some embodiments, the number, size, and arrangement of the sub-pixelswill be such that it is preferable to limit each activated pixel of thecalibration pattern to a single channel R, G, B, etc. This ensures anyslight difference between sub-pixel locations of R, G, B, and any slightdifferences in the PSFs for each channel R, G, B, etc. will accuratelybe associated with each measurement separately. The calibration patternor patterns should have enough red, green, and blue calibration pixelsto adequately characterize the display panel 220 in accordance with theforegoing.

Once the calibration pattern has been displayed and captured 306, aseries of display test patterns is displayed by the display panel 220and images are captured by the camera 230. Each test pattern of theseries of display test patterns include pixels having non-zero greyscaleluminance spaced apart far enough so that some portion of each image ofeach pixel of the pattern displayed on the display panel 220 as itappears in the captured images, which are blurred according to the PSF,do not interfere or overlap with images of the other pixels of thepattern. As described above, intentional defocusing of the camera 230 issuch that images of each illuminated pixel of the display panel 220appears as a spread out blurred image of that pixel according to the PSFand problems due to aliasing (moire) are avoided. In some embodiments,the activated pixels of the display test patterns are arranged in aspaced rectilinear array or a rectangular lattice. In such embodimentsthe activated pixels are located at corners of an imaginary grid whichwould result from imaginary lines drawn through the rows and columns ofactivated pixels and is also known as a dot grid. Other regular latticesinclude triangular, and diamond pattern lattices. Any sparse set ofactivated pixels of sufficient spacing may be used whether arranged in aregular or irregular lattice.

The series of display test patterns are such that each pixel 110 of thedisplay panel 220 may be corrected with correction data based onmeasurements in the form of the captured images by the camera 230 of thedisplay panel 220 displaying the display test patterns. Preferably, theresolution of the display test pattern is the same as the resolution ofthe display panel 220.

In some embodiments, the series of display test patterns are such thateach pixel of the display panel 220 is activated at more than one levelof greyscale luminance. In some embodiments, this is done separately foreach channel R, G, B, etc. In some embodiments, the series of displaytest patterns include, for every pixel, at least one pattern having thatpixel activated at a fixed first greyscale luminance value P1 and atleast one other pattern having that pixel activated at a fixed secondgreyscale luminance value P2. The first and second fixed greyscaleluminance values P1, P2 used to activate the pixel are generally chosenbased on what levels of greyscale are desired to exhibit the greatestuniformity. In some embodiments, the series of display test patternsinclude, for every pixel, at least one pattern having that pixelactivated at a fixed relatively low greyscale luminance value P1 (forexample 10 percent of the possible maximum greyscale luminance value)and at least one other pattern having that pixel activated at a fixedrelatively high greyscale luminance value P2 (for example 80 percent ofthe possible maximum greyscale luminance value). Over the series ofdisplay test patterns, every single pixel is programmed at least oncewith each of P1 and P2 and corresponding resulting luminances of thepixel caused by programming the pixel with P1 and P2 are determined fromthe images of that pixel in those captured images of the display panel220 displaying those display test patterns with that pixel at values P1and P2. Pixels of the display test patterns having values P1 or P2 arereferred to hereinafter as “regular test pixels”.

The number of display test patterns and the levels of the illuminatedpixels therein depends upon the technique used to correct the data usedto program each pixel. The example embodiments which follow correct thedisplay panel non-uniformity by determining the DAC (Digital to AnalogueConverter) signal which corrects the luminance non-uniformity of thepanel by determining information about the DAC signal to luminance scalefactor. The scale factor, once determined is used to scale the DACcorrection signal to the luminance non-uniformity so that the correctionapplied corrects for the non-uniformity. This scale factor is obtainedby also including in the series of test patterns, a subset of pixels(for example ⅓ or ¼ of the total number of pixels of the display panel220) throughout the display test patterns such that the pixel isactivated with greyscale luminance values near P1 and P2, i.e. at a DACsignal level of P1 or P2 changed by some small Δ (+Δ or −Δ). In someembodiments, Δ is a small percentage of the maximum greyscale luminancelevel (such as 1%), and in other embodiments, Δ is on the order of thesmallest incremental digital value in the DAC signal. In someembodiments, this is done separately for each channel R, G, B, etc. Thedifference between the luminance produced by the pixels of the displaypanel 220 displaying a value of P1 (or P2) and the luminance produced bythe pixels of the display panel 220 displaying a value of P1 +Δ or −Δ(or P2 +Δ or −Δ) allows extraction of the scale factor between the DACsignal and measured luminance at P1 (or P2) and therefore can be used totranslate luminance non-uniformity into a correction signal. In someembodiments, the series of display test patterns includes pixels ofgreyscale luminance levels including both +Δ and −Δ about values P1 andP2. In some embodiments, instead of small positive and negative changessymmetrically about the midpoint PX, the small positive change +deltaand the small negative change are −Delta not identical in magnitude. Insome embodiments, the multilevel pixels about P1 are not at the samelocations as the multilevel pixels about P2. In some embodiments themultilevel pixels include multilevel sample greyscale luminances of morethan two levels for each PX.

The subset of pixels of the display test patterns is chosen to be lessthan the total number of pixels of the display panel 220 because thescale factor does not deviate greatly pixel to pixel and generallyexhibits localized uniformity but exhibits global non-uniformity overthe entire display panel 220. Although multilevel data for only thosedisplay panel pixels which display the subset of pixels (hereinafter“multilevel pixels”) of the display test patterns is extracted, thescale factors corresponding to P1 and P2 for all pixels may be estimatedwith use of an interpolation algorithm, such as bilinear interpolationfor a rectilinear subset, or any other method appropriate for theparticular arrangement of the subset of pixels. In some embodiments themeasured luminances are interpolated first, and scale factors for allpixels are determined from those values, while in other embodiments thescale factors are determined first for some pixels and then interpolatedfor all pixels.

To correct the panel within the set of all possible input DAC, P1 and P2should be chosen to be far apart, and value 1 should be chosen lowenough to approximate properly panel non-uniformity for all possible DACvalues. In other embodiments, regular test pixels include pixels at Nlevels, P1, PN, and the multilevel pixels include pixels at 2N levels,namely, at P1+Δ, P1Δ, . . . , PN+Δ, PN−Δ.

Once all of the display test patterns have been displayed and captured308, correction data is determined 310 from a processing by the opticalcorrection processing 240 of all of the images taken by the camera 230.The calibration image or images taken by the camera of the calibrationpattern or patterns are processed. As described above, the calibrationimage is processed to establish the location of individual pixels on thedisplay panel 220 and to correct for any geometrical distortion such asrotation, tilt, and skew. For calibration patterns with sparse activatedpixels whose images in the calibration image do not overlap, the PSFs ofvarious regions of the display panel 220 are directly observable fromthe images of the blurred activated pixels and may be substantiallydirectly extracted from the calibration image. Generally, data forming amapping of display panel 220 pixel locations to image pixel locations inimages captured by the camera 230 are produced along with data whichallow the extraction of an estimate of the PSF for every pixel of thedisplay panel 220.

Once the calibration image is processed, the captured images of thedisplay test patterns displayed by the display panel 220 are processed.Using the known location within the captured image of each pixel of thedisplay panel 220, and using the expected PSF in the area of the knownlocation, a luminance of each pixel of the display panel 220 isextracted. In some embodiments, an acquisition kernel, acquisitionfilter, or integration window is used to extract a value of theluminance of each pixel of the display panel 220. In some embodiments, adeblurring, sharpening, or deconvolution algorithm is used to extract avalue of the luminance of each pixel of the display panel 220. In someembodiments, this is done separately for each channel R, G, B, etc. Insome embodiments the acquisition kernel is centered on the expectedknown location of each pixel being measured, and uses either anunweighted or weighted integral of a size and shape taking into accountthe PSF of the particular area of the pixel and the spacing in thecaptured image between the activated pixels of the test pattern. In someembodiments in which the defocusing and spacing of the pixels causesimages of the pixels to partially overlap, the acquisition kernel isweighted so as to ignore the areas of overlap, or is otherwiseconfigured and processed so that areas of overlap do not introduceerrors in the determination of the luminance of each pixel. In someembodiments the acquisition kernel is generally rectangular and in otherembodiments it is generally circular. Other acquisition kernals arepossible, and in general they are sized, shaped, and weighted inaccordance with the PSF and the spacing in the captured image of theactivated pixels of the test pattern.

The luminances L1 and L2 for every pixel of the display panel 220 whendriven respectively at P1 and P2 are determined. These correspond to theluminance measurements of the pixels 110 of the display panel 220 whichdisplayed the regular test pixels of the display test patterns. Furtherluminances L1a, L1b, L2a, and L2b for the sparse subset of the pixels ofthe display panel 220 when driven respectively by P1+Δ, P1-Δ, P2+Δ, andP2-Δ are also determined. These correspond to the luminance measurementsof the pixels 110 display panel 220 which displayed the multilevel testpixels of the display test patterns. For every pixel of the display,scale factors S1 and S2 associated respectively with DAC signal P1 andP2 may be determined from measured luminances L1a, L1b, L2a, and L2bwhen available for that pixel, or are interpolated from scale factors S1and S2 of other pixels of the display for which measured luminances L1a,L1b, L2a, and L2b are available or are calculated from L1a, L1b, L2a,and L2b values interpolated from L1a, L1b, L2a, and L2b of other pixelsof the display for which those measurements exist. In embodiments wherethe multilevel pixels about P1 are not at the same locations as themultilevel pixels about P2, spatial interpolation of the luminances L1a,L1b, L2a, and L2b at pixels which have the values can be used todetermine a luminance L1a, L1b, L2a, and L2b for the pixel in question,in order to determine the scale factors.

In one embodiment, S1 is determined from measured luminances L1, L1a,and L1b and Δ as:

$\begin{matrix}{{S1} = {\frac{1}{2}\left( {\frac{\Delta}{{L1a} - {L1}} + \frac{\Delta}{{L1} - {L1b}}} \right)}} & (1)\end{matrix}$

and S2 is determined from measured luminances L2, L2a, and L2b and Δ as:

$\begin{matrix}{{S2} = {\frac{1}{2}\left( {\frac{\Delta}{{L2a} - {L2}} + \frac{\Delta}{{L2} - {L2b}}} \right)}} & (2)\end{matrix}$

Analogous scale factors may be determined similarly for embodimentshaving regular test pixels which include pixels at N levels, P1, PN, andthe multilevel test pixels include pixels at 2N levels, namely, at P1+Δ,P1−Δ, . . . , PN+Δ, PN−Δ. In some embodiments, processing is performedseparately for each channel R, G, B, etc. Higher order approximationsmay be obtained for embodiments with more than two multilevel samplesabout each point PX, e.g. for four multilevel pixels P1+Δ, P1−Δ, P1+δ,P1-δ.

As can be seen from equations (1) and (2), the scale factors S1 and S2quantify the relationship, respectively at DAC points P1 and P2, betweena change in DAC signal value and the resulting change in luminance.

The measured luminance L1 at P1 is compared to a known expectedluminance to determine an actual deviation in luminance. The actualdeviation in luminance and the scale factor S1 are used to determine acorrected DAC signal CP1, i.e. the corrected signal which causes thepixel to produce the desired actual luminance for greyscale luminancevalue P1. Similarly a corrected DAC signal CP2 is calculated forcorrecting greyscale luminance value P2. From these two points (P1, CP1)and (P2, CP2) a linear relationship of the form CPn=B*Pn+C is determinedand hence for any desired greyscale luminance value Pn, a corrected DACvalue CPn may be calculated.

The correction data for each pixel therefore includes the slope B andoffset C, as determined above using L1, L2, S1, and S2, to determine thecorrected DAC value CPn from any input greyscale luminance value Pn.

The correction data, once determined 310 is transferred 312 to thedisplay 250 via the controller 202 and stored in memory 106.

During operation of the display 250, correction data stored in memory106 is used by the controller 202 or in combination with a separatecompensation block (not shown) to correct image data input to thedisplay 250 for display on the display panel 220. In some embodiments,the slope B and offset C are calculated for each pixel of the displaypanel 220, using for example interpolation, prior to being stored in thedisplay 250, to reduce processing required of the display 250 whilecorrecting DAC signals. For embodiments having regular test pixels whichinclude pixels at N levels (where N>2), and multilevel test pixels at 2Nlevels, the correction data includes higher order coefficients of(N−1)th order polynomials directly analogous to the linear relationshipdescribed above. In some embodiments, the correction data include slopeB and offset C (or analogous higher order coefficients) for eachchannel, R, G, B, etc.

When the pixels 110 of the display panel 220 are driven by the correctedsignals, the image displayed by the display panel 220 exhibits greatlyreduced or negligible non-uniformity.

As described herein above, the calibration patterns along with thedisplay test patterns should include the calibration pixels, the regulartest pixels, and the multilevel pixels, while ensuring that in eachpattern the pixels are spaced far enough apart so images of theseactivated pixels in the captured images have at least some portion whichdoes not overlap with blurred images of other pixels. In some embodimentthese pixels are displayed separately for each of the channels R, G, B,etc. The ordering and grouping of the pixels in the display testpatterns does not matter. In some embodiments, each display test patternonly has pixels of the same channel, in other embodiments only of thesame level (e.g. P1 or P2), while in other embodiments each display testpattern includes pixels of more than one or of all channels, and inother embodiments each test pattern includes pixels of both levels. Asdescribed above each pixel of the display panel 220 should be driven atthe two levels P1, P2 (or more in the case of P1, PN) and a subset ofpixels should be driven as multilevel pixels to provide data for thescale factors S1, S2 (or possibly S1, . . . , SN). Although the orderingand grouping of the pixels in the test patterns does not matter, ideallythe spacing is minimized to minimize the total number of display testpatterns displayed. This reduces the capture time of the process.

In some embodiments, the pixels of the display test patterns displayedand captured 308 are grouped into specific types of display testpatterns. FIG. 4 illustrates a specific method 400 of displaying andcapturing 308 display test patterns in which the regular test pixels andmultilevel pixels have been grouped in specific ways. In someembodiment, all of the following is performed separately for eachchannel of the display R, G, B, etc.

At 402 a first set of sparse flat test patterns are displayed, eachpattern of the set such that all of the activated pixels of the patternare at level P1. The number of display test patterns in the first set ofsparse flat patterns depends upon the spacing of pixels in the arraywhich avoids or produces the expected amount of overlap. For example, ifeach flat test pattern has activated pixels in a square rectilineararray or rectangular lattice spaced apart vertically and horizontally bythree inactive pixels, then the first set of sparse flat patterns wouldinclude a total of 16 test patterns, each shifted vertically and orhorizontally with respect to each other. The first set of sparse testpatterns, ensures the regular test pixel at level P1 is measured forevery pixel of the display panel 220.

At 404 a first set of one or more multilevel patterns is displayed, eachpattern of the set such that all of the activated pixels of the patternare at level P1 plus or minus a small Δ. The desired number of pixels(equivalently the density of pixels) for the subset constituting themultilevel pixels about P1 will vary depending upon the exhibited amountof nonuniformity in the scale factor for the type of particular displaypanel 220 being measured. The number of display test patterns in thefirst set of one or more multilevel patterns depends upon the spacing ofpixels in the array which avoids or produces the expected amount ofoverlap, and the desired number of pixels (or the desired pixel density)in the subset constituting the multilevel pixels about P1. Inembodiments where the scale factor exhibited across the display panel220 is generally uniform, only one multilevel pattern for P1 may berequired. The first set of one or more multilevel patterns (P1±Δ),ensures all desired multilevel pixels for the display panel 220 aboutlevel P1 are measured.

At 406 a second set of sparse flat test patterns are displayed, eachpattern of the set such that all of the activated pixels of the patternare at level P2. The number of display test patterns in the second setof sparse flat patterns depends upon the spacing of pixels in the arraywhich avoids or produces the expected amount of overlap. For example, ifeach flat test pattern has activated pixels in a square rectilineararray or rectangular lattice spaced vertically and horizontally by threepixels, then the second set of sparse flat patterns would include atotal of 16 test patterns, each shifted vertically and or horizontallywith respect to each other. The second set of sparse test patterns,ensures the regular test pixel at level P2 is measured for every pixelof the display panel 220.

At 408 a second set of one or more multilevel patterns is displayed,each pattern of the set such that all of the activated pixels of thepattern are at level P2 plus or minus a small Δ. The number of displaytest patterns in the second set of one or more multilevel patternsdepends upon the spacing of pixels in the array which avoids or producesthe expected amount of overlap, and the desired number of pixels (ordesired pixel density) in the subset constituting the multilevel pixelsabout P2. Generally this number of pixels (or pixel density) will be thesame as that for the number of pixels in the subset constituting themultilevel pixels about P1, and for the same reasons. In embodimentswhere the scale factor exhibited across the display panel 220 isgenerally uniform, only one multilevel pattern for P2 may be required.The second set of one or more multilevel patterns (P2±Δ), ensures alldesired multilevel pixels for the display panel 220 about level P2 aremeasured.

While particular implementations and applications of the presentdisclosure have been illustrated and described, it is to be understoodthat the present disclosure is not limited to the precise constructionand compositions disclosed herein and that various modifications,changes, and variations can be apparent from the foregoing descriptionswithout departing from the spirit and scope of an invention as definedin the appended claims.

1-28. (canceled)
 29. An optical correction method for correcting fornon-uniformity of an emissive display panel having pixels, each pixelhaving a light-emitting device, the method comprising: arranging acamera in front of the display panel; displaying from each pixel of afirst sparse set of activated pixels of the display: a first greyscaleluminance value of a relatively low greyscale luminance value, and asecond greyscale luminance value of a relatively high greyscaleluminance value which is spaced apart from the first greyscale luminancevalue by a relatively large greyscale luminance value difference;displaying from pixels of a second sparse set of activated pixels of thedisplay: a third greyscale luminance value greater or less than thefirst greyscale luminance value by a first relatively small greyscaleluminance value difference, the relatively large greyscale luminancevalue difference being greater than said first relatively smallgreyscale luminance value difference, displaying from pixels of a thirdsparse set of activated pixels of the display: a fourth greyscaleluminance value greater or less than the second greyscale luminancevalue by a second relatively small greyscale luminance value difference,the relatively large greyscale luminance value difference being greaterthan said second relatively small greyscale luminance value difference;measuring a luminance of each pixel of the first, second, and thirdsparse sets of activated pixels of the display with the camera whiledisplaying the first greyscale luminance, the second greyscaleluminance, the third greyscale luminance, and the fourth greyscaleluminance, to generate luminance measurement data including respectivelyfirst luminance measurement data, second luminance measurement data,third luminance measurement data, and fourth luminance measurement data;and determining from said luminance measurement data with use of adetermined comparison between the first and third luminance measurementdata and a determined comparison between the second and fourth luminancemeasurement data, correction data for correcting non-uniformity ofimages displayed in the display panel.
 30. The optical correction methodof claim 29, further comprising: defocusing the camera such that thefocal point of the camera lies outside of a plane passing through thelight-emitting devices of the display panel, the defocusing such thatindividual pixels of the display panel are blurred in images of thedisplay panel captured by the camera; wherein said measuring a luminanceof each of said pixels of the first, second, and third sparse sets ofactivated pixels of the display comprises capturing images of thedisplay with the camera; wherein each of the first, second, third, andfourth greyscale luminance values are different from a greyscaleluminance of a flat background greyscale displayed between saidactivated pixels, wherein locations of said activated pixels are spacedapart such that in each captured image, at least one portion of eachblurred image of each activated pixel does not overlap with a blurredimage of another activated pixel; wherein said displaying said first,second, third, and fourth greyscale luminance values includesprogramming each pixel of said first, second, and third sparse set ofactivated pixels by: displaying a plurality of test patterns while saidcapturing said images, each of said displayed test patterns comprising aset of activated image pixels at image locations corresponding to saidlocations of said activated pixels, for programming each pixel of thefirst, second, and third sparse sets of activated pixels to display saidfirst, second, third, and fourth greyscale luminance values, saidactivated image pixels of the plurality of displayed test patternsincluding: regular test pixels, for programming each activated pixel todisplay said first and second greyscale luminance values; and multilevelpixels, for programming each activated pixel to display said third andfourth greyscale luminance values.
 31. The optical correction method ofclaim 30, wherein a resolution of the camera is less than twice aresolution of the display panel, and wherein the amount of blurring inimages of the display panel captured by the camera is sufficient toavoid aliasing in the captured images of the display panel.
 32. Theoptical correction method of claim 30, wherein said locations of saidactivated pixels are arranged in a diamond or rectangular lattice. 33.The optical correction method of claim 30, further comprisingdetermining correction data for an activated pixel of the display panelwith use of the first and second luminance measurement data, and withuse of luminance measurements of pixels throughout the display panelwhen displaying the multilevel pixels of the displayed test patterns.34. The optical correction method of claim 33, wherein said activatedimage pixels of the plurality of the displayed test patterns comprisecalibration pixels, the method further comprising: determining locationsof the activated pixels as they appear in the captured images of thedisplayed test patterns; and determining at least one point spreadfunction exhibited by blurred images of activated pixels in the capturedimages, wherein the activated image pixels of the plurality of displayedtest patterns are spaced apart such that in the captured images, blurredimages of each calibration pixel does not overlap with blurred images ofany other activated pixel.
 35. The optical correction method of claim34, wherein each of the luminance measurements of each of the regulartest pixels and each of the multilevel pixels is performed with use ofan acquisition kernel determined from at least one of a spacing of theactivated pixels and the at least one point spread function.
 36. Theoptical correction method of claim 29, wherein the relatively lowgreyscale luminance value is substantially 10 percent of the maximumpossible greyscale luminance value, and the relatively high greyscaleluminance value is substantially 80 percent of the maximum greyscaleluminance value.
 37. The optical correction method of claim 29, whereinthe relatively small greyscale luminance value is one of substantially 1percent of the maximum possible greyscale luminance value and thesmallest incremental digital value of possible greyscale luminancevalues.
 38. The optical correction method of claim 33, wherein all ofsaid regular test pixels of the relatively low greyscale luminance valueare displayed in a first set of sparse flat test patterns, wherein allof said regular test pixels of the relatively high greyscale luminancevalue are displayed in a second set of sparse flat test patterns,wherein all of said multilevel pixels having a greyscale luminance valuegreater or less than the relatively low greyscale luminance value aredisplayed in a first set of multilevel patterns, and wherein all of saidmultilevel pixels having a greyscale luminance value greater or lessthan the relatively high greyscale luminance value are displayed in asecond set of multilevel patterns.
 39. The optical correction method ofclaim 29, further comprising correcting image data with use of thecorrection data prior to driving the pixels to display an imagecorresponding to the image data.
 40. An optical correction system forcorrecting non-uniformity of an emissive display having pixels, eachpixel having a light-emitting device, the system comprising: a cameraarranged in front of the display for capturing images of the displaypanel while each pixel of a first sparse set of activated pixels of thedisplay displays: a first greyscale luminance value of a relatively lowgreyscale luminance value, and a second greyscale luminance value of arelatively high greyscale luminance value which is spaced apart from thefirst greyscale luminance value by a relatively large greyscaleluminance value difference; and while each pixel of a second sparse setof activated pixels of the display displays: a third greyscale luminancevalue greater or less than the first greyscale luminance value by afirst relatively small greyscale luminance value difference, therelatively large greyscale value difference being greater than saidfirst relatively small greyscale luminance value difference; and whileeach pixel of a third sparse set of activated pixels of the displaydisplays: a fourth greyscale luminance value greater or less than thesecond greyscale luminance value by a second relatively small greyscaleluminance value difference, the relatively large greyscale luminancevalue difference being greater than said second relatively smallgreyscale luminance value difference; and optical correction processingcoupled to the camera and for receiving from the camera captured imagesof each pixel of the first, second, and third sparse sets of activatedpixels of the display while displaying the first greyscale luminance,the second greyscale luminance, the third greyscale luminance and thefourth greyscale luminance, to generate luminance measurement dataincluding respectively first luminance measurement data, secondluminance measurement data, third luminance measurement data, and fourthluminance measurement data; determining from said luminance measurementdata, correction data with use of a determined comparison between thefirst and third luminance measurement data and a determined comparisonbetween the second and fourth luminance measurement data for correctingnon-uniformity of images displayed in the display; and